The focus of this proposal is to develop strategies to transfer and effectively express genes in alveolar macrophages (AM), the pulmonary representative of the mononuclear phagocyte system. Based on preliminary data from our laboratory that adenovirus (Ad) gene transfer vectors can be used to transfer and express genes in murine and human AM that Ad vectors with modified fiber sequences are more effective in this process. and that Ad vector-mediated gene expression can be upregulated in AM by changing the extracellular milieu of the AM the central hypothesis of this proposal is that by understanding the biology of Ad-mediated gene transfer to precursor, resting and activated AM, modifications can be made to the structure of the vector. the environment in which gene transfer takes place, and the composition of the promoter in the expression cassette to be transferred to enable effective genetic modification of AM. To evaluate this hypothesis. this proposal has four specific aims. First, to define the biology of Ad vector entry and translocation in precursor, resting and activated AM relevant to effective nuclear transfer and expression of the transgene carried by the Ad vector. Second, to modulate Ad vector-mediated transfer and expression in AM by altering the structure of the vector and/or modulating the environment in which the vector interacts with the AM. Third, to evaluate the persistence of the Ad vector genome and the expression of the vector transgene in precursor. resting and activated AM in vitro and in vivo. Fourth, to develop strategies to confine the expression of Ad vector mediated gene transfer only to AM, and strategies to modulate control of expression of the transferred gene. In the context of the important role of AM in health and disease, it is rational to hypothesize that modification of the genetic repertoire of AM should be useful in the therapy of a number of acute and chronic lung disorders.